1. Field of the Invention
The invention relates to a downhole safety valve for a subterranean well, and more particularly to a safety valve utilizing electrical mechanism, controlled from the surface by electromagnetic waves, for opening and closing the valve and for locking the valve in an open position.
2. Summary of the Prior Art
The employment of a downhole safety valve is well known for subterranean oil and gas wells. Such valve, which can comprise a plug or poppet type, a sleeve valve, a flapper valve, or a ball valve, is normally positioned downhole to close the bore of the tubing string leading from one or more production zones to the well surface. Such safety valves are normally biased to a fail safe condition, i.e., energized means will shift the valve to its closed position upon any significant reduction in the opening force applied to the valve structure.
The more common type of safety valves utilizes a control fluid pressure to effect the shifting of the valve to its open positon. Such control fluid pressure is supplied through a small control conduit which is run into the well concurrently with the production tubing. Necessarily, such conduit is susceptible to damage during the run-in process, or joints in the conduit may develop leaks. In any event, the loss of integrity of the conduit will effect the immediate closing of the safety valve and the well is essentially out of operation until the entire tubing string has been pulled from the well and the necessary repairs made.
To offset the difficulties involved in the utilization of a control pressure conduit, it has been previously proposed that the downhole safety valve be actuated from its closed to its open position by a downhole solenoid which is supplied with electrical power from the surface by an electric line. The same problem of potential damage to the electric line during the run-in process exists with this arrangement and, of course, any abrasion of the insulation of the electric line during the run-in process leads to the possibility of short circuits developing in the electric line, again requiring that the entire tubing string be pulled from the well to effect the necessary repairs.
It is often necessary to run tools down through the production conduit and the open downhole safety valve to effect treatment of the production formation. Under such conditions, it is highly desirable that the safety valve be positively locked in an open position so that unexpected fluctuations in well pressure will not cause the safety valve to attempt to close when a wireline or a treatment conduit is passing through the valve. A variety of fluid pressure or mechanically actuated latching mechanisms have heretofore been proposed to effect the locking of a downhole safety valve in an open position. U.S. Pat. No. 4,579,177 discloses a solenoid actuated locking mechanism for a downhole safety valve. Such solenoid is energized by an electric line leading to the well surface, hence is subject to the problems mentioned above involved in maintaining the integrity of an electric line run into a subterranean well concurrently with production tubing.
There is a need, therefore, for a subsurface safety valve which is controllable from the surface to move from a closed to an open position, and also incorporates a locking mechanism, controllable from the well surface, for selectively maintaining the safety valve in a locked-open position, which does not depend upon the utilization of a control fluid pressure conduit or an electric line extending from the safety valve to the well surface to effect its operation.
In recent years, systems have been developed for transmitting relatively low frequency electromagnetic waves through ground or water by launching and propagating magnetic waves of generally vertical magnetic polarization through the intervening subterranean region of earth or water between a pair of magnetic dipole antennas. See, for example, U.S. Pat. No. 3,967,201 to RORDEN.
In co-pending application, Ser. No. 730,397, filed May 3, 1985, and now U.S. Pat. No. 4,736,791, entitled "Improvements in Subsurface Device Actuators," and assigned to a wholly owned subsidiary of the assignee of the instant application, there is disclosed a system for actuating a downhole safety valve between open and closed positions in response to low frequency electromagnetic waves received by a downhole antenna from a surface located transmitting antenna. Such apparatus incorporates a downhole battery but does not employ the battery for effecting the shifting of the safety valve from its closed to its open position, an act which requires a substantial amount of electrical energy. Instead, the system disclosed in such application relies upon fluid pressure to effect the shifting of the safety valve from a spring bias closed position to an open position.
Such co-pending application does, however, disclose a downhole battery and a locking solenoid selectively energized by such battery in response to electromagnetic wave signals generated by a surface transmitter. The energization of the solenoid effects the operation of a locking mechanism to secure the safety valve in its open position. Thus, while some of the disadvantages of the above described prior art systems have been overcome, the construction disclosed in the aforesaid pending application still requires the utilization of fluid pressure to effect the shifting of the safety valve to an open position.